As an image used for medical diagnosis in the related art, for example, a tomographic image of a subject photographed by an X-ray CT (Computed Tomography) apparatus, an MRI (Magnetic Resonance imaging) apparatus, or the like is known. In addition, a computer-aided detection apparatus (Computer-Aided Detection; hereinafter, referred to as CAD) has been developed which analyzes such a medical image using a computer, detects a lesion candidate from the shading, and presents it to a doctor. The CAD detects an image region (hereinafter, referred to as a lesion candidate region), which is presumed to be a lesion, automatically on the basis of the shape characteristic or density characteristic of the lesion in order to ease the burden on the doctor.
For example, Patent Document 1 or Patent Document 2 discloses a method of analyzing and displaying the constriction rate of a blood vessel. Specifically, in Patent Document 1, the constriction rate is calculated by assuming the shape of a temporary normal blood vessel on the basis of blood vessel shape information created from the image data and comparing the sizes of the sectional areas or diameters of the blood vessel and the temporary normal blood vessel with each other to detect a constricted portion.
In addition, in Patent Document 2, the constriction rate is calculated by correcting distortion of the blood vessel shape, assuming the shape of a temporary normal blood vessel on the basis of the blood vessel shape after correction, and detecting a constricted portion using the blood vessel and the temporary normal blood vessel.